The production of ethylene and propylene, herein referred to as “light olefins,” is typically conducted at very large scales to achieve efficient economy of operation. The conversion of oxygenates to olefins (OTO) and more specifically, methanol to olefins (MTO), has been a subject of great interest in the emerging field of olefin production. The OTO and MTO processes typically use molecular sieve catalysts, especially silicoaluminophosphate (SAPO) molecular sieves.
One goal during the conversion of oxygenates to olefins is to maximize the production of light olefins, preferably ethylene and propylene, and to minimize the production of methane, ethane, propane, and C5+ materials. Increasing the selectivity of preferred hydrocarbon products such as ethylene and/or propylene from the conversion of an oxygenate using a molecular sieve catalyst composition is described in U.S. Pat. No. 6,137,022, and PCT WO 00/74848 published Dec. 14, 2000, which are all herein incorporated by reference.
Production of ethylene and propylene reaches a maximum when a certain level of coke is maintained on the catalyst. U.S. Pat. No. 6,023,005, incorporated herein by reference, teaches the desirability of providing carbonaceous deposits, or coke levels, for oxygenates to olefins conversion processes, in the range of 2 wt % to about 30 wt %, based on the total reaction volume of coked catalyst to promote selectivity to light olefins.
U.S. Patent Application Publication No. 2003/0125598 discloses a process for making an olefin product from an oxygenate-containing feedstock. The application disclosure introducing regenerated catalyst particles into a reaction zone to provide a catalyst mixture in an amount sufficient to provide an average coke loading on the catalyst mixture.